1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, in particular, a current limiting mechanism for noise reduction in a charge pump circuit, which restricts noise generation in the charge pump circuit in a semiconductor integrated circuit device.
2. Description of the Related Art
FIG. 2 shows a conventional charge pump circuit. In the charge pump circuit, a pump capacitor is temporarily charged by an input power source and then, a voltage of the pump capacitor is further stepped up to charge an output capacitor. The charge pump circuit allows a current to directly flow into the pump capacitor and into the output capacitor, thereby causing a large peak current to instantly flow (see U.S. Pat. No. 5,550,728, for example).
However, the current directly flows from the input power source into the pump capacitor and into the output capacitor in the conventional charge pump circuit. This causes a large peak current to instantly flow upon charging the capacitor. As a result, a voltage of the input power source varies to generate noise, which faces the possibility that other circuits connected to the input power source shared with the charge pump circuit erroneously operate.